Research On Equalization Circuit Of Secondary Used Battery Energy Storage System

In recent years,the new energy electric vehicle industry has developed rapidly under the guidance of the state and the promotion of the market.After several years of development,the power battery of electric vehicle will be decommissioned on a large scale.The recovery and secondary utilization of electric vehicle batteries become an urgent problem to be solved.Recycled batteries can be reused in energy storage systems with lower battery performance requirements,which can help promote the application of energy storage technology and realize effective utilization of energy resources.This thesis aims to improve the battery inconsistency in the energy storage system with secondary used batteries,and studies balancing method for secondary used batteries in the application of energy storage.Based on the capacity inconsistent of secondary used battery and the requirement of energy storage system grouping,this thesis designs a multi-stage equalization scheme with characteristics of large current,multi-port and synchronous control.The equalization scheme can meet the equalization needs of all battery cells,improve the capacity utilization of battery packs and reduce the system loss.Starting from the basic working principle of dual-port Buck-Boost converter,this thesis introduces the basic principle,control method and working mode of current control in multi-port synchronous equalization circuit,and deduces the theoretical relationship of switch's duty cycle combining with the analysis of switching state.The real-time control for equalization current of all batteries can be realized through synchronous control for switches.And then,a simulation platform is built to verify the synchronous control of the equalization current and the independent control of the multi-level equalization.By analyzing the inconsistency between batteries,this thesis introduces the influence of capacity inconsistent of secondary used batteries on the performance of battery packs.Moreover,the thesis expounds the balancing control strategies of battery SOC,capacity and voltage,and puts forward improved methods for traditional SOC equalization control in order to improve the equalization speed.Several balancing control strategies are verified and analyzed by simulation,and the multi-level equalization scheme is also verified by simulation.The simulation results prove the effectiveness of the control strategy in this thesis.The structure and control scheme of multi-port synchronous control equalization circuit are introduced through the design of hardware and software.Using the experimental platform,the synchronous current control is experimentally verified,and the main experimental waveforms are analyzed.Through the experiment of synchronous current control with two ports,four ports and six ports,it is proved that the multi-port synchronous equalization circuit topology adopted in this thesis is extensible and the control method is generally applicable.Finally,the effectiveness of voltage and SOC equalization control strategies are verify through experiment.The experimental results show that the improved equalization control strategy designed in this thesis can effectively achieve the equalization control,and it has good applicability in the case of high equalization speed requirements.